1. Field of the Invention
The present invention relates to techniques for providing a gamma correction of video signals in which, in the signal transmission path, a luminance signal and at least one signal containing an item of color information are multiplicatively corrected.
2. Description of the Prior Art
The picture tube of a television receiver possesses a nonlinear relationship between the electric input signal supplied thereto and the emitted luminance. The camera tube of a television camera, in many cases, also exhibits a nonlinear relationship between the quantity of light supplied thereto and its electric output signal. Normally, one endeavors to achieve a linear transmission characteristic, which is obtained by means of the so-called gamma correction, also referred to as gradation correction.
In color television, gamma correction is also required for the color information, where the correction factors for the individual color component signals (RGB) differ from each other. Generally, the gamma correction is carried out in the television camera, either in that special camera tubes are provided for the individual color component signals, and both the luminance signal and color component signals can be produced and corrected discretely, or in that, in the case of a single tube color television camera, the color component signals are derived from a chrominance signal obtained from the camera tube by way of a matrix specified for gamma correction, and are then reassembled by way of a matrix to form the corrected chrominance signal.
The latter of the two methods mentioned above is expensive because of the utilization of a matrix. It is less expensive to carry out the gamma correction directly for the chrominance signal in dependence upon the luminance signal. That is to say that the individual color component signals are no longer separately corrected, but only the overall chrominance signal in which they are contained is corrected. However, because of the differing transmission characteristics of the individual colors, this technique results in the fact that a linear transmission characteristic for the entire transmission is no longer possible.